Vulcanization of rubber



v Patented Jan. 17, 1928.

UNITED- STATES PATENT OFFICE.

WINFIELD SCOTT, OF AKRON, OHIO, A SSIGNOR TO THE RUBBER SERVICE LABORA- TORIES COMPANY, OF AKRON, OHIO, A.CORPORATION OF OHIO.

'VULCANIZA'IION OF RUBBER.

No Drawing.

The presentinvention is directed to the art of manufacturing vulcanized rubber."

The invention is particularly concerned with the production of a vulcanized rubber of high quality, and possessing desirable commercial characteristics, by a process-wherein a new type of accelerator is used for the vulcanization step. The manufacture and means of employing the new preferred class of acceleratorsis fully set forth hereinafter and will be readily understood by the following description and examples.

Certain mercapto compounds such as mercapto-benzothiazole heretofore have been described as of value in accelerating the vulcanization of a rubber mix. I Moreover, mercapto compounds, that is compounds containing a C-SH grouping, inwhich the hydrogen of the sulphydrate group is suiticiently acidic to react with organic bases products useful as rubber vulcanization accelerators as are disclosed in a copending application Serial.No. 61,587 filed by me October 9, 1925. k

I have now further found that compounds obtained by the action of aldehydes upon the present applicatiomwhich is a division of this last mentioned application, comprises the use of such compounds in the manufacture of vulcanized. rubber products. The invention will bereadily understood from the following description and examples illustra;

tive of the process and product claimed.

The following is .one example of a preferredmethod of manufacturing one of my new type of accelerating compounds.

One molecular-proportion of a mercaptocompound, for example 167 parts by weight of mercaptobenzo-thiazole, is combined with one molecular proportion of an organic base, for example 239 parts by weight of di-o-tolyl-guanidine, by heating the sub may be reacted with various bases to form Application filed May 6, 1927. Serial No. 189,462.

- is allowed to cool and solidify and is then ground to a fine powder. This powder is then treated with one molecular proportion parts) of croton-aldehyde or with an equivalent proportion of some other aldehyde, preferably of the aliphatic series.

Inasmuch as the reaction product of an organic base and a mer'capto compound, when combined as described with an aldehyde,. evolves more or less heat, it is desir able, particularly when an aldehyde boiling at moderate temperatures be employed. that the reaction be carried out within a tightly enclosed vessel. or that the vessel or chamher be equipped'with a cooling means to con- .dense and return by reflux any aldehyde that vaporizes. The reactingmixture soon becomes pasty, and rapidly becomes so viscous that some heating is usually necessary to keep the mixture fluid enough to permit stirring. After the reaction with the aldehyde is completed. the liquid mass is withdrawn from the react on chamber, and is allowed to cool and solidify. The solid ma.- terial, in the case of the croton-aldehyde reaction product of the di-orthotolyl guanidine salt of mercapto-benzo-thiazole, is a hard slightly yellowish resin which can be readily ground and is then ready for use as a vulcanization accelerator.

It is of course possible to replace the in gredients particularly mentioned in the example given above with equivalent materials. In place of mercapto-benzo-thiazole, I may employ mercapto-tolyl-thiazole, thio-cresol, thio-phenol, butyl-mercaptan. di-n-aminod-i-thio-carbamic acids, or in fact, any mercapto compound wherein the C-SH group present "possesses suflicient acidity to react with an organic base. Thus, I may also use thio-acet anilide, which in one of its isomeric forms possesses the structure of a mercapas given. Thus, I may likewise employ di,

phenyl-guanidine,

" elongation of 810%. When .0.5 parts of the aldol reaction product of the salt formed by tan. Similarly, other bases than di-o-tolylguanidine may be employed in the example piperidine, enthanolamine, as well as other organic bases, particularly the primary and secondary amines. It is also possible to use other aldehydes than croton-aldehyde in the preparation, of my final product. Thus, such aldehydes as aldol, acetaldehyde, propional (lehyde, heptaldehyde, and other saturated and unsaturated aldehydes, particularly of the aliphatic series maybe used.

The aldehyde reaction products of the salts obtained by reacting mercaptans with bases, comprise a class of-compounds particularly useful as accelerators of the vulcanization of rubber. Their usefulness" for this purpose is greatly enhanced becauseof their resinous nature whereby their ready and complete dispersion into the rubber mix can be accomplished. One method of employing this new type of compound in a rubber mix is illustrated by the following exam le, wherein 100-parts of rubber, such aspa e crepe rubber, 5 parts of zinc oxide 3.5 parts of sulfur, and 0.3 parts of one of the compounds hereinbefore described, for example, the cr'oton-aldehyde derivative of the'reaction product of di-o-tolyl-guanidine and mercapto-benzo-thiazole, are compounded together in the usual manner on the differential mixing mills. The rubber compound so prepared was then vulcanized in the usual manner at the temperature given by steam at a ressure of 10 pounds per square inch. A ter heating under these conditions for a period of 30 minutes, the vulcanized product was found to possess a modulus at 700% elongation, of 1635 pounds per equare inch, a tensile strength at break of 3120 pounds per square inch and an ultimate the combination of mere 'pto-benzo-thiazole and di-PhenyLguanidine' iS substituted for the accelerator employed in the example above,and the mixture heated at a temperature of 20 pounds of steam per square inch for 15 minutes, the product is found to possess a tensile strength of 2855 pounds per squared inch and an ultimate elongation of 870%.

The aldol reaction product of the salt formed by the combination of mercaptobenzo-thiazole and di-o-tolyl-guanidine,may be employed in the example given above in lace of the accelerator employedtherein.

is material can be prepared by adding one molecular proportion ofaldol to the melted reaction product of equal molecular proportions of rhercapto-benzo-thiazole and di-o-tolyl-guanidine. The mass is maintained in a molten condition and is stirred the usual manner.

until the mixture is homo neous and com- I may be used in the proportion of 0.5 parts of the accelerator with 100 parts of pale crepe rub ber, 5 parts of zinc oxide, and 3.5 parts of sulfur, and the mix vulcanized in When the composition is heated in a press for a period of about minutes at the temperature given by 20 pounds of steam pressure per square inch the product is found to have a modulus of 3030 at 700% elongation, a tensile strength at break of 4280 pounds per square inch, and an ultimate elongation of 780%. Equally favorable results are realized when the com- U position is heated at higher temperatures, although in such cases a completely vulcanized-product is, of course, obtained in a shorter period of time, than that given in the example. I

Another material included among my new type of accelerators is obtained by: reacting 0.5 molecular proportions of he taldehyde with one molecular proportion .0 the product obtained-by melting'to ether (and'combining in the manner ereinbefore set forth) equal molecular proportions of mercapto to yl thiazole (2 methyl -mercaptobenzo thiazole) and di ortho tolyl guanidine. This product, when compounded in the usual manner in the proportion of 0.5 parts accelerator, with"100"parts of rubber, 5 parts of zinc oxide, and 3 parts of sulfur, and vulcanized in a pressat a temperature given by 40 pounds of'steam per square inch, gives a vulcanized product of high quality after heating for approximately 60 minutes.

This particular accelerator is somewhat scribed. For example, croton-aldehyde has been reacted upon the reaction product of piperidine and mercapto benzo thiazole; croton-aldehyde has been reacted upon the reaction product of di-ortolyl-guanidine and thio-acet-anilide; aldol has been reacted upon the reaction product of ethanol-amine and thio-cresol; propion ic aldehyde has been reacted on the di-o-tolyl-guanidine Salt of cll-n -butyl-amino-di-thio earbamic acid. These various compounds have been found to possess valuable and desirable vulcaniza- 't1on accelerating properties when employed in a rubber mix. I

' 'cinnamic aldehyde, or other aldehydes may be used. In case a readily volatilizable aldehyde be used in reacting on the molten salt, it is desirable that the reaction be carried out within an enclosed chamber. or that a stream of the aldehyde vapor be bubbled through the melted mixture. Broadly then, my invention comprises the use in the rubber vulcanizing process of relatively small quantities of accelerating compounds pro.- duced by the reaction of aldehydes, preferably of the aliphatic series with salts formed by the action of organic buses upon mercaptan compounds and derivatives of the mor captans containing the C- SH group.

While, in describing my invention, I have referred to'certain specific details, it will be understood that these are illustrative only, and not limitative. Nor is my invention to be considered as dependent upon the accuracy of any theory or reason suggested to explain the advantageous results realized. On the contrary, the invention is to be regarded as limited only as defined in the following claims, in which it is my intention to claim all novelty inherent in my invention as broadly as is permissible in view of the prior art.

What I claim is:

1. The process of vulcanizing rubber which comprises heating a mixture of rubber and sulphur in the presence of an accelerator including an aldehyde derivative of the reaction product of an organic base and a inercapto compound containing a C-SH grouping.

'2. The process of vulcanizing rubber which comprises heating a mixture of rubber and sulphur in the presence of an accelerator including an aldehyde derivative of the reaction product of a substituted guanidine and an aromatic mercaptan containing a 'G-SH grouping.

3. The process of vulcanizing rubber which com rises heating amixture of rub ber and su phur in the presence of an accelerator including an aldehyde derivative of the reaction product of an aryl-substitutedguanidine and a derivative of an aromatic mercaptan containing a C-SH grouping.

4. The process of vulcanizing rubber which comprises heating a mixture of rub ber and sulphur in thepresence of an accelerator including an aliphatic aldehyde derivative of the reaction product of an aryldi-substituted-guanidine and an aromatic mercaptan containing the C-SH grouping. 5. The process of vulcanizing rubber which comprises heating a mixture of rubber and sulphur in the presence of an accelerator including an aldehyde derivative of an organic salt produced by the neutralization of a compound containing a C-SH grouping with an organic base.

8. The process of vulcanizing rubber which comprises heating a mixture of rubber and sulphur in the presence of an accelorator including an aliphatic aldehyde derivative of an organic salt produced by the neutralization of a compound containing a C-SH grouping with a nitrogen containing basic compound.

9. The process of vulcanizing rubber which comprises heating a mixture of rubber and sulphur in the presence of an accelerator including an unsaturated aliphatic aldehyde derivative of the reaction product of an organic compound of basic nature with an aryl thiazole.

10 The process of vulcanizing rubber which comprises heating a mixture of rubber and sulphur in the presence of an accelerator including a croton-aldehyde derivative of the reaction product of a di-arylsubstituted-guanidine with an aryl thiazole.

l'ljThe process of vulcanizing rubber which comprises heating a mixture of rubber and sulphur in the presence of an accel-' orator including an aldehyde derivative of the reaction product of an amine with an organic compound containing the sulphydrate group.

12. The. process of vulcanizing rubber which comprises heating a mixture of rubber and sulphur in the presence or an accel- .erator including an aldehyde derivative ofthe reaction product of an organic derivative of ammonia with a mercapto compound containing a C-SH grouping.

13. The vulcanized rubber product produced by heating a mixture of rubber and sulphur in the presence of an accelerator ncluding an aldehyde derivative of the reaction product of an organic base and a mercapto compound containing a C-SH group 1ng.. I

14. The vulcanized rubber product produced by heating a mixture of rubber and sulphur in the presence or an accelerator including an aldehyde derivative of the reacaryl-di substituted-guanidine and an arotion product of a substituted guanidine and an aromatic mercaptan containing a C-SH grouping. .v

15. The vulcanized rubber product produced by heating a mixture of rubber and sulphur in the presence of an accelerator including an aldehyde derivative of the reaction product of an aryl-substituted-guanidine and a derivative of an armoatic mercaptan containing a C-SH grouping.

16. The vulcanized rubber product produced by heating a mixture of rubber and sulphur in the presence of an accelerator including an unsaturated aliphatic aldehyde derivative of the reaction product of an matic mercaptan containing a C-SH group- 17. The vulcanized rubber product produced by heating a mixture of rubber and eluding an unsaturated aldehyde derivative of the reaction product of an organic compound of basic nature with an aryl thiazole. 19. The vulcanized rubber product produced by heating a mixture of rubber and sulphur in the presence of an accelerator including an aldehyde derivative of the reaction product of an organic derivative of ammonia'with a mercapto compound containing a C-SH grouping.

In testimony whereof I have afiixed my signature.

WINFIELD SCOTT. 

